Heat input control method for multi-electron-beam powder bed melting additive manufacturing process

Abstract

The invention discloses a heat input control method for a multi-electron-beam powder bed melting additive manufacturing process, which adopts a finite element simulation means to control heat input in the additive manufacturing process and can be applied to research and development of powder bed preheating process parameters in the multi-electron-beam powder bed melting additive manufacturing forming process. Through cooperative work of a forming electron beam and a preheating electron beam, a temperature field is dynamically regulated and controlled in combination with finite element simulation, and the problems of large temperature gradient, high residual stress and multiple crack defects in a traditional process are solved; the electron beam is preheated to continuously heat the non-melting area, double-beam energy distribution is optimized in combination with an energy balance equation, and the forming quality and the process efficiency are remarkably improved.

Description

Technical Field

[0001] The present invention relates to a method for controlling heat input in a multi-electron beam powder bed fusion additive manufacturing process. Background Art

[0002] The electron beam powder bed fusion (EB-PBF) additive manufacturing technology has advantages such as high vacuum degree and high tissue purity, and also has the characteristic of real-time regulating the temperature of the powder bed by high-frequency scanning of the electron beam, which is particularly suitable for the preparation of large and complex structures of difficult-to-weld high-temperature materials.

[0003] During the electron beam selective melting forming process, problems such as powder collapse and warping deformation of the formed part often occur. Powder collapse refers to the phenomenon that before melting, due to the action of the electron beam on the metal powder and the interaction force (Coulomb repulsion) between the powder and the electrons, the metal powder deviates from its original position. The warping deformation of the formed part is usually caused by thermal stress, solidification shrinkage force, and tissue stress induced by a large temperature gradient.

[0004] Research shows that before electron beam selective melting forming, by applying a preheating treatment below the powder melting temperature on the powder bed, the adhesion of the powder bed can be improved, the powder can be firmly attached to the bottom layer, thereby enhancing the powder's anti-collapse ability. At the same time, this preheating can reduce the temperature gradient, optimize the temperature distribution of the powder bed, ensure a more uniform temperature field of the part during the forming process, and thus effectively avoid the occurrence of warping deformation.

[0005] Traditional single electron beam selective melting forming uses one electron gun to complete the preheating-forming process, with a long preheating waiting time and relatively single temperature control means. The multi-electron beam powder bed fusion additive manufacturing process changes the traditional single electron gun into multiple electron guns in pairs, and each group of electron guns consists of a preheating electron gun and a forming electron gun; the preheating electron gun outputs a preheating electron beam and works continuously, responsible for preheating the powder bed and controlling heat input during the forming process; the forming electron gun outputs a forming electron beam and is responsible for forming the powder, and only works when the powder preheating is completed and forming is required. This requires designing a method for controlling heat input in a multi-electron beam powder bed fusion additive manufacturing process. Summary of the Invention

[0006] To solve the defects of the prior art, the present invention provides a method for controlling heat input in a multi-electron beam powder bed fusion additive manufacturing process, including the following steps:

[0007] Step 1: Divide the forming area into multiple micro-element areas of a specific size;

[0008] Step 2: For each micro-element region, based on the vacuum forming environment of electron beam powder bed fusion additive manufacturing and the actual forming temperature uniformity, only consider the surface thermal radiation of this single micro-element region, without considering convective heat transfer and lateral heat conduction, and establish a heat dissipation equation for the forming process;

[0009] Step 3: For each micro-element region, except for the formed part, it is in a state of energy dissipation during the preheating-forming process, and the heat input is the preheating electron beam and the forming electron beam power input; based on the heat balance theory, combined with the forming scanning time of each layer of the workpiece, establish a heat input-energy dissipation model, solve the reference heat input to obtain the beam current size required for preheating, that is, obtain the reference beam current;

[0010] Step 4: Establish a finite element simulation model for the multi-electron beam selective melting process, use the reference beam current size obtained in Step 3 for simulation, and design and plan a variety of preheating gun scanning paths according to the characteristics of the formed workpiece, the forming electron beam path, etc., and simulate to obtain the temperature field distribution of the entire area;

[0011] Step 5: Dynamically adjust the heat input, identify the low-temperature region and generate a preheating electron beam heat compensation path. If the detected temperature gradient exceeds the threshold, automatically increase the preheating power or reduce the scanning pitch.

[0012] Preferably, in Step 1, the size of the micro-element region is determined according to the position and size of the formed workpiece, similar to the mesh division in finite element analysis.

[0013] Preferably, in Step 3,

[0014] The temperature field equation is:

[0015]

[0016] The boundary conditions are:

[0017]

[0018] The input power is:

[0019]

[0020] Preferably, in Step 5, the preheating electron beam heat compensation path adopts a spiral or grid scanning mode.

[0021] The advantages and beneficial effects of the present invention are as follows: A method for controlling the heat input of a multi-electron beam powder bed fusion additive manufacturing process is provided. By using finite element simulation means to control the heat input during the additive manufacturing process, it can be applied to the research and development of the powder bed preheating process parameters in the multi-electron beam powder bed fusion additive manufacturing process. Through the collaborative work of the forming electron beam and the preheating electron beam, combined with finite element simulation to dynamically regulate the temperature field, the problems of large temperature gradient, high residual stress and many crack defects in the traditional process are solved; the preheating electron beam continuously compensates the heat of the non-molten area, and combines the energy balance equation to optimize the energy distribution of the double beams, significantly improving the forming quality and process efficiency. Specific Embodiments

[0022] The following combines examples to further describe the specific embodiments of the present invention. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0023] The specific technical solutions implemented by the present invention are as follows:

[0024] The present invention provides a method for controlling the heat input of a multi-electron beam powder bed fusion additive manufacturing process;

[0025] The multi-electron beam powder bed fusion additive manufacturing process uses multiple electron guns in pairs. Each group of electron guns consists of a preheating electron gun and a forming electron gun; the preheating electron gun outputs a preheating electron beam and works continuously, responsible for preheating the powder bed and controlling the heat input during the forming process; the forming electron gun outputs a forming electron beam and is responsible for forming the powder, and only works when the powder preheating is completed and forming is required;

[0026] The heat input control method includes the following steps:

[0027] Step 1: Divide the forming area into multiple micro-element areas of a specific size. The size of the micro-element area is determined according to the position and size of the formed workpiece, similar to the mesh division in finite element analysis;

[0028] Step 2: For each micro-element area, based on the vacuum forming environment of the electron beam powder bed fusion additive manufacturing and the actual temperature uniformity of the forming, only consider the surface heat radiation of this single micro-element area, without considering convective heat transfer and lateral heat conduction, and establish a heat dissipation equation for the forming process;

[0029] Step 3: For each micro-element area, except for the formed part, it is always in an energy dissipation state during the preheating-forming process, and the heat input is the power input of the preheating electron beam and the forming electron beam; based on the heat balance theory, combined with the forming scanning time of each layer of the workpiece, establish a heat input-energy dissipation model, and solve the reference heat input to obtain the beam current size required for preheating, that is, the reference beam current;

[0030] The temperature field equation in Step 3 is as follows:

[0031]

[0032] The boundary conditions in Step 3 are as follows:

[0033]

[0034] The input power in Step 3 is as follows:

[0035]

[0036] Among them,

[0037] is the overall conservation of the temperature change of a certain microelement, T is the temperature;

[0038] i refers to the top layer;

[0039] Lt is the thickness of the powder layer to be fused;

[0040] is the rate of change of temperature in the z direction (assuming the temperature in the xy direction remains unchanged);

[0041] λ met is the thermal conductivity of the material; σ met is the thermal radiation coefficient of the metal surface;

[0042] σ pow is the thermal radiation coefficient of the powder surface; h pow is the heat transfer coefficient from the object to the powder;

[0043] T(iLt) is the temperature of the object surface when the i-th layer melts;

[0044] Tsur(i) is the ambient temperature affecting its surface during the fusion of the powder layer (which can be measured on the heating shield);

[0045] Tbott(i) is the temperature at the bottom of the object before starting the i-th layer;

[0046] P in is the input power;

[0047] A(iLt) is the surface area of the object in the i-th layer;

[0048] Step 4: Establish a finite element simulation model for the multi-electron beam selective melting process, perform the simulation using the benchmark beam current magnitude obtained in Step 3, design and plan multiple preheating gun scanning paths based on the characteristics of the formed workpiece, the path of the forming electron beam, etc., and simulate to obtain the temperature field distribution of the entire area;

[0049] Step 5: Dynamically adjust the heat input, identify the low-temperature area and generate a preheating electron beam heat compensation path (helical or raster scanning mode). If the detected temperature gradient exceeds the threshold, automatically increase the preheating power or reduce the scanning pitch.

[0050] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for controlling heat input in a multi-electron beam powder bed fusion additive manufacturing process, characterized in that, It includes the following steps: Step 1: Divide the forming area into multiple micro-regions of a specific size; Step 2: For each micro-region, based on the vacuum forming environment of electron beam powder bed fusion additive manufacturing and the actual temperature uniformity of forming, only consider the surface thermal radiation of this single micro-region, without considering convective heat transfer and lateral heat conduction, and establish a heat dissipation equation for the forming process; Step 3: For each micro-region, except for the forming part, it is in an energy dissipation state during the preheating-forming process, and the heat input is the preheating electron beam and the forming electron beam power input; based on the heat balance theory, combined with the forming scanning time of each layer of the workpiece, establish a heat input-energy dissipation model, solve the reference heat input to obtain the beam current size required for preheating, that is, obtain the reference beam current; Step 4: Establish a finite element simulation model for the multi-electron beam selective melting process, use the reference beam current obtained in Step 3 for simulation, design and plan multiple preheating gun scanning paths according to the characteristics of the formed workpiece and the forming electron beam path, and simulate the temperature field distribution of the entire area; Step 5: Dynamically adjust the heat input, identify the low-temperature region and generate a preheating electron beam heat compensation path. If the detected temperature gradient exceeds the threshold, increase the preheating power or reduce the scanning pitch.

2. The method for controlling heat input of the multi-electron beam powder bed fusion additive manufacturing process according to claim 1, characterized in that In Step 1, the size of the micro-region is determined according to the position and size of the formed workpiece.

3. The method for controlling heat input of the multi-electron beam powder bed fusion additive manufacturing process according to claim 1, wherein, In Step 3, the temperature field equation is:

4. The method for controlling heat input in the multi-electron beam powder bed fusion additive manufacturing process according to claim 3, wherein In Step 3, the boundary conditions are:

5. The method for controlling heat input of the multi-electron beam powder bed fusion additive manufacturing process according to claim 4, characterized in that, In Step 3, the input power is:

6. The method for controlling the heat input of the multi-electron beam powder bed fusion additive manufacturing process according to claim 1, characterized in that, In Step 5, the preheating electron beam heat compensation path adopts a spiral or grid scanning mode.

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